The Li+-Na+ exchange and Na+-K+-Cl- cotransport systems in essential hypertension

New Insight of Li-Doped Cu2ZnSn(S,Se)4 Thin Films: Li-Induced Na Diffusion from Soda Lime Glass by a Cation-Exchange Reaction

In our recent report (ACS Appl. Mater. Interfaces 2016, 8, 5308), Li⁺ ions had been successfully incorporated into the lattice of the selenized Cu₂ZnSn(S,Se)₄ thin film on a quartz substrate by substituting equivalent Cu⁺ ions, and Li⁺ ions was also found to have the little effect on the crystal growth and defect passivation. To further improve the cell performance of Li-doped CZTSSe devices, we conducted the same experiments on the sodium-rich soda-lime glass (SLG) substrate in this study, instead of sodium-free quartz substrate. Surprisingly, only trace amounts of Li (Li/Cu molar ratio ∼1 × 10^-4) were detected in the final CZTSSe thin films; meanwhile, a large amount of sodium was present on the surface and at the grain boundaries of the selenized thin films. A Li/Na exchange mechanism is used to explain this phenomenon. Only on the sodium-free substrate can Li⁺ ions enter the CZTSSe host lattice, and doping Li⁺ ions on the SLG substrate are nearly identical to doping Na⁺ ions.

Primate response to angiotensin infusion and high sodium intake differ by sodium lithium countertransport phenotype

An increased level of sodium-lithium countertransport (SLC) activity has been associated with salt-sensitive hypertension. Previous findings have suggested that dysregulation of the renin-angiotensin-aldosterone system (RAAS) may be involved in the mechanism linking elevated SLC activity and hypertension. Therefore, baboons with different levels of SLC activity were given two diets differing in sodium content, with and without an angiotensin II (ANG II) infusion, to investigate the relationship between SLC activity, the RAAS, and physiological regulation by sodium. Although we anticipated that high SLC activity would be associated with inappropriate function of the RAAS and greater arterial pressure sensitivity to dietary sodium and ANG II and that low SLC activity would be associated with the least BP sensitivity, we found that the low SLC phenotype correlated with BP sensitivity similar to the high SLC phenotype, and the normal SLC phenotype showed the least BP sensitivity to dietary sodium and ANG II.

The metabolic syndrome: an emerging risk state for cardiovascular disease

The common clustering of glucose intolerance, insulin resistance, abdominal adiposity, elevated blood pressure, and low HDL cholesterol is referred to as metabolic syndrome. Individuals with this syndrome have an increased risk of developing cardiovascular disease (CVD). The World Health Organisation and the National Cholesterol Education Programme’s Adult Treatment Panel III (NCEP-ATP III) have outlined specific diagnostic criteria for the diagnosis of the metabolic syndrome to help in the Identification of this syndrome in clinical practice. While the WHO criteria were specifically developed for use in research, the NCEP criteria are useful in clinical diagnosis of the metabolic syndrome. The metabolic syndrome is amenable to lifestyle modifications such as increased physical activity, weight loss, and possibly intake of low-glycemic foods. Drug therapy may be used to treat individual components of the syndrome such as elevated blood pressure and dyslipidemia. To control elevated glucose levels (when there is failure of lifestyle modification), medications such as metformin, thiazolidinedione derivatives and alpha glucosidase inhibitors may be used.

Elevated erythrocyte sodium-lithium counter-transport in hypertensive patients with non-insulin-dependent diabetes mellitus

Increased erythrocyte (RBC) sodium-lithium (Na-Li) counter transport (CT) has been reported to be a genetic marker for essential hypertension (EHT). In addition, increased RBC Na-Li CT has been demonstrated in insulin-dependent diabetic (IDDM) patients with nephropathy, indicating that a predisposition to hypertension may cause renal damage and impaired renal function. Therefore, the present study was designed to determine RBC Na-Li CT in subjects with essential hypertension (EHT) and non-insulin-dependent diabetics (NIDDM) with or without hypertension (NIDDMHT or NIDDMNT), using the method of Canessa et al. with a slight modification by flame photometry and expressed as nmol Li/5 x 10(6) RBC/h. Na-Li CT in patients with EHT (0.159 +/- 0.051 (S.D.), n = 26) or NIDDMHT (0.168 +/0 0.083, n = 42) was higher than that in NIDDMNT patients (0.127 +/- 0.059, n = 27, P < 0.05). Among the NIDDMHT patients, those with clinical nephropathy had the same levels of Na-Li CT as those without nephropathy. When the NIDDM patients were divided into two groups with or without insulin treatment, the Na-Li CT in hypertensives was higher than that in normotensives, irrespective of whether or not they were on insulin therapy. Addition of insulin to RBCs in vitro did not augment the Na-Li CT activity. These results suggest that an increase of Na-Li CT may not be due to the stimulatory effect of endogenous or exogenous insulin, and reflect a genetic predisposition for hypertension, and hence diabetic nephropathy, not only in IDDM but also NIDDM patients.

Insulin resistance in systemic hypertension: pharmacotherapeutic implications

Systemic hypertension, a vascular disease with multiple origins, now is being linked to subtle abnormalities in glucose metabolism, which include insulin resistance and hyperinsulinemia. These conditions often occur together in patients with obesity, noninsulin-dependent diabetes, or both. Hyperinsulinemia and insulin resistance may cause systemic hypertension through multiple mechanisms. Insulin has a salt-retaining effect on the kidney. Also, insulin can augment catecholamine release, increase vascular sensitivity to vasoconstrictor substances, and decrease vascular sensitivity to vasodilator substances. In addition, insulin can increase production of tissue growth factors and help retain sodium and calcium in cells. Insulin resistance in patients can be treated with regular aerobic exercise, weight reduction, and a high-fiber diet. Pharmacologic approaches include hypoglycemic drugs, weight-reducing agents, and certain antihypertensive drugs that may have a favorable impact on both blood pressure and insulin resistance.

Is increased erythrocyte sodium-lithium countertransport a useful marker for diabetic nephropathy?

Genetic predisposition to essential hypertension has been proposed as a risk factor for the development of diabetic nephropathy in type 1 (insulin-dependent) diabetes mellitus. An increased sodium-lithium countertransport activity (NaLiCT) has been suggested as a genetic marker for essential hypertension. We therefore evaluated NaLiCT in diabetic patients with (N = 39) or without (N = 23) diabetic nephropathy (DNP), patients with non-diabetic renal diseases (N = 42) and in healthy controls (N = 24). The NaLiCT was elevated in both diabetic patient groups compared to healthy controls (median 244; range 134 to 390 mumol.liter cells-1.hr-1), but was not different in patients with DNP (median 314; range 162 to 676), without DNP (median 325; range 189 to 627) and patients with non-diabetic renal disease (median 300; range 142 to 655). The genetic predisposition to DNP is illustrated by the fact that diabetic sibs of probands with DNP showed a higher occurrence of DNP than diabetic sibs of patients without DNP. We analyzed whether familial DNP clustered with an increased NaLiCT. The NaLiCT in sibs concordant for the presence of DNP (N = 10; median 307; range 217 to 428 mumol.liter cells-1.hr-1) was not significantly different from that in sibs concordant for absence of DNP (N = 15; median 279; range 189 to 442). We conclude that erythrocyte sodium-lithium countertransport activity cannot be used as a marker to identify patients at risk for the development of diabetic nephropathy.

Acute effects of angiotensin-converting enzyme inhibitor on erythrocyte sodium ion transport in essential hypertension

The acute effects of angiotensin-converting enzyme inhibitor, captopril, on sodium ion transport systems were investigated in essential hypertensive and normotensive subjects. The passive sodium efflux through the erythrocyte membrane was significantly higher and erythrocyte sodium-potassium cotransport was lower in patients with essential hypertension when compared with normal subjects. However, sodium-potassium pump activity and sodium-lithium countertransport did not differ significantly between the hypertensive patients and the normal subjects. Immediately after captopril administration, erythrocyte passive sodium efflux and sodium-potassium cotransport returned to normal levels in the hypertensive subjects. Although the plasma renin activity and plasma aldosterone concentration were altered by captopril, they did not correlate with changes in any sodium transport system. These results suggest that the changes in sodium transport systems which occur immediately after captopril administration may contribute, at least in part, to its antihypertensive action.

Correlates of sodium-lithium countertransport. Findings from the Gubbio Epidemiological Study. The Gubbio Collaborative Study Group

BACKGROUND

Numerous reports have presented evidence for a positive association between the maximal velocity of the sodium-lithium countertransport (Na-Li CT) in erythrocytes and hypertension. The nature of this association remains to be clarified.

METHODS AND RESULTS

This report presents correlates of Na-Li CT in a population sample of 3,591 people aged 5-74 years. Males had higher mean age-specific levels of Na-Li CT than females except for the 5-14-year age stratum. In adults aged 25-74, for both men (n = 1,044) and women (n = 1,192), body mass index, plasma uric acid and glucose, alcohol consumption, and red blood cell mean corpuscular volume were positively related to countertransport in multivariate analyses; plasma high-density lipoprotein (HDL) cholesterol and plasma potassium were inversely related. Plasma non-HDL cholesterol was independently and directly related to Na-Li CT in women, and plasma sodium was inversely associated with Na-Li CT in men. These relations prevailed for men when persons with hypertension were excluded from the analyses and prevailed in part for women. When stepwise regression analyses were done for all men and women combined (n = 2,236), sex ceased to be significantly related to countertransport with plasma uric acid and alcohol intake in the model. In adults of either sex, no independent association was detected between Na-Li CT and age, heart rate, or the ratios of sodium to potassium or of sodium to creatinine in overnight untimed urine.

CONCLUSIONS

In both sexes, Na-Li CT is significantly and independently associated with a number of metabolic variables (plasma uric acid, plasma glucose, body mass index, plasma potassium, and life-style habits [e.g., alcohol intake]). Further research is needed to elucidate the meaning of the significant associations between Na-Li CT and the foregoing variables (all of them also related to blood pressure).

Sodium-lithium countertransport and cardiorenal abnormalities in essential hypertension

The rate of red blood cell sodium-lithium countertransport is elevated only in a subgroup of patients with essential hypertension. We have therefore compared renal and cardiac function and morphology in two groups of hypertensive patients with high (n = 23) or normal (n = 22) sodium-lithium countertransport (mean +/- SEM: 0.61 +/- 0.10 versus 0.29 +/- 0.07 mmol/l red blood cells.hr). The two groups were similar in age, sex distribution, body mass index, smoking habit, duration of hypertension, and actual levels of untreated blood pressure. Hypertensive patients with elevated sodium-lithium countertransport activity showed elevated glomerular filtration rate (118 +/- 2 versus 109 +/- 2 ml/min.1.73 m2; p less than 0.001), albumin excretion rate (23 +/- 3 versus 14 +/- 2 micrograms/min; p less than 0.001), larger kidney volume (250 +/- 15 versus 203 +/- 13 ml.1.73 m2; p less than 0.01), lower lithium clearance rate (26.7 +/- 0.3 versus 28.9 +/- 0.3 ml/min.1.73 m2; p less than 0.01), and higher total body exchangeable sodium (2,716 +/- 33 versus 2,485 +/- 41 mmol.1.73 m2; p less than 0.01). Left ventricular mass index (139 +/- 6 versus 119 +/- 6 g/m2; p less than 0.05), relative wall thickness (0.39 +/- 0.05 versus 0.29 +/- 0.04 cm; p less than 0.001), and left posterior wall plus intraventricular septum thickness (2.02 +/- 0.04 versus 1.76 +/- 0.03 cm; p less than 0.05) were also higher in patients with high sodium-lithium countertransport. Hypertensive patients with normal sodium-lithium countertransport had renal and cardiac parameters similar to those of a normotensive control group (n = 21) except for a higher glomerular filtration rate and left ventricular mass index.(ABSTRACT TRUNCATED AT 250 WORDS)

Linkage of MN locus and erythrocyte lithium-sodium countertransport in Tecumseh, Michigan

Human essential hypertension is a family of diseases; one subtype has an increased maximum velocity for red blood cell lithium-sodium countertransport activity. To begin the localization of the gene or genes responsible for this phenotype, we examined the association of blood pressure, lithium-sodium countertransport, and two genetic markers previously associated with hypertension--the MN blood group antigen (chromosome 4) and the plasma protein haptoglobin (chromosome 18)--in a population-based sample of 592 young adults from Tecumseh, Mich., the site of an ongoing cardiovascular epidemiological investigation. Our results suggest that the relation between MN phenotype and systolic blood pressure is significantly different and oppositely directed in men and women. Analysis of data available from previous examinations revealed that similar blood pressure differences related to MN phenotype had been present at least a decade earlier in both men and women. There also was a significant relation between systolic blood pressure and haptoglobin phenotype for the combined group of men and women. In addition to having high systolic blood pressure, men with the MM phenotype had significantly elevated red blood cell lithium-sodium countertransport activity. In studies of brother-brother pairs, we found evidence for significant genetic linkage between the MN locus and red blood cell lithium-sodium countertransport activity.

Red blood cell lithium-sodium countertransport in the tecumseh blood pressure study

Human essential hypertension has more than one cause, but to dissect out subtypes, markers are required. The maximal activity of red blood cell lithium-sodium countertransport has been shown to be increased in hypertensive patients in case-control and population-based studies; in the latter, its distribution is a mixture of two overlapping but distinguishable subpopulations. In the present study, we classified 705 participants in the Tecumseh Blood Pressure Study as having either normal (mean, 0.234 mmol/l cells/hr; n = 614) or high (mean, 0.463 mmol/l cells/hr; n = 91) red blood cell lithium-sodium countertransport to determine if the red blood cell marker is associated with distinctive physiological characteristics. We found that subjects with elevated lithium-sodium countertransport have higher average blood pressure and a greater prevalence of hypertension than those with normal countertransport and that elevated blood pressure had been present since youth. Hemodynamically, the high countertransport group is characterized by elevated vascular resistance, whereas sympathetic nervous system activity appears to be slightly depressed. Subjects with increased lithium-sodium countertransport, compared with those with normal countertransport, have significantly lower average left ventricular mass index and only very infrequently demonstrate left ventricular hypertrophy. Our results support the usefulness of measurements of the maximal activity of red blood cell lithium-sodium countertransport as a way of distinguishing subgroups in the population. Our data are consistent with the idea that subjects with an elevated maximal activity for red blood cell lithium-sodium countertransport are a subset of the population with a genetic lesion that predisposes them to the development of essential hypertension.

Kinetic abnormalities of the red blood cell sodium-proton exchange in hypertensive patients

The present study was designed to examine the kinetics of Na(+)-H+ exchange in red blood cells of normotensive and hypertensive subjects and its relation to the previously reported abnormalities in Na(+)-Li+ exchange. The Na(+)-H+ antiporter activation kinetics were studied by varying cell pH and measuring net Na+ influx (mmol/l cell x hr = units) driven by an outward H+ gradient. The Na(+)-Li+ exchange was determined at pH 7.4 as sodium-stimulated Li+ efflux. Untreated hypertensive patients (n = 30) had a higher maximal rate of Na(+)-Li+ exchange (0.43 +/- 0.05 versus 0.26 +/- 0.02 units, p less than 0.0003), a higher maximal rate of Na(+)-H+ exchange (62.3 +/- 6.2 versus 47 +/- 4 units; p less than 0.02), but a similar affinity for cell pH compared with normotensive subjects (n = 46). The cell pH activation of the Na(+)-H+ antiporter exhibited a lower Hill coefficient than that of normotensive subjects (1.61 +/- 0.12 versus 2.56 +/- 0.14; p less than 0.0001). This index of occupancy of internal H+ regulatory sites was found reduced in most of the hypertensive patients (73%) whether their hypertension was untreated or treated. Hypertensive patients with Na(+)-Li+ exchange above 0.35 units (0.68 +/- 0.057 units, n = 16) did not exhibit elevated maximal rates of Na(+)-H+ exchange (57.3 +/- 10 units, NS) in comparison with those with Na(+)-Li+ exchange below 0.35 units (66.4 +/- 7.6 units, n = 26), but both groups exhibited reduced Hill coefficients. Hypertensive patients with enhanced Na(+)-H+ exchange activity (more than 90 units) had normal maximal rates of Na(+)-Li+ exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum insulin, insulin sensitivity, and erythrocyte sodium metabolism in normotensive and essential hypertensive subjects with and without overweight

Increased insulin circulating levels and perturbations of intracellular sodium metabolism have been reported in essential hypertensive patients, leading to postulate their involvement in the pathophysiology of the disease. In-vitro studies have shown that insulin modulates the activity of some transmembrane sodium transporters. The aim of this investigation was to assess in subjects with essential hypertension and/or overweight, the levels of fasting serum insulin, the activity of sodium transporters and their possible relationships. In 18 lean normotensive, 12 overweight normotensive, 18 untreated lean essential hypertensive, and 16 untreated overweight essential hypertensive subjects, we measured the fasting levels of blood glucose and serum insulin, and calculated the glucose/insulin ratio as an index of sensitivity to insulin. In addition, in the red blood cells of these subjects, we evaluated the maximal rate of ouabain-sensitive Na/K pump, furosemide-sensitive outward Na/K cotransport, Nai/Lio countertransport, and the constant rate of passive permeability to Na. When compared to lean normotensive, overweight normotensive, lean hypertensive, and overweight hypertensive subjects exhibited significantly higher fasting insulin levels, with lower glucose/insulin ratio. No significant difference was found in the activity of Na/K pump, Na/K cotransport, and passive permeability to Na. The Nai/Lio exchange was significantly increased in both hypertensive groups. Mean blood pressure correlated positively and independently with body mass index and fasting insulinemia, and inversely with the glucose/insulin ratio. No relationships were found between blood pressure, fasting insulin levels or glucose/insulin ratio and the activity of sodium transport systems. We conclude that hyperinsulinemia and insulin resistance are associated with essential hypertension independently of overweight. These data lend support to the hypothesis that insulin is involved, concurrently with other factors, in the pathogenesis of essential hypertension in both lean and obese subjects.

Interactions of external and internal H+ and Na+ with Na+/Na+ and Na+/H+ exchange of rabbit red cells: evidence for a common pathway

We have studied the kinetic properties of rabbit red cell (RRBC) Na+/Na+ and Na+/H+ exchanges (EXC) in order to define whether or not both transport functions are conducted by the same molecule. The strategy has been to determine the interactions of Na+ and H+ at the internal (i) and external (o) sites for both exchanges modes. RRBC containing varying Nai and Hi were prepared by nystatin and DIDS treatment of acid-loaded cells. Na+/Na+ EXC was measured as Nao-stimulated Na+ efflux and Na+/H+ EXC as Nao-stimulated H+ efflux and delta pHo-stimulated Na+ influx into acid-loaded cells. The activation of Na+/Na+ EXC by Nao at pHi 7.4 did not follow simple hyperbolic kinetics. Testing of different kinetic models to obtain the best fit for the experimental data indicated the presence of high (Km 2.2 mM) and low affinity (Km 108 mM) sites for a single- or two-carrier system. The activation of Na+/H+ EXC by Nao (pHi 6.6, Nai less than 1 mM) also showed high (Km 11 mM) and low (Km 248 mM) affinity sites. External H+ competitively inhibited Na+/Na+ EXC at the low affinity Nao site (KH 52 nM) while internally H+ were competitive inhibitors (pK 6.7) at low Nai and allosteric activators (pK 7.0) at high Nai. Na+/H+ EXC was also inhibited by acid pHo and allosterically activated by Hi (pK 6.4). We also established the presence of a Nai regulatory site which activates Na+/H+ and Na+/Na+ EXC modifying the affinity for Nao of both pathways. At low Nai, Na+/Na+ EXC was inhibited by acid pHi and Na+/H+ stimulated but at high Nai, Na+/Na+ EXC was stimulated and Na+/H+ inhibited being the sum of both pathways kept constant. Both exchange modes were activated by two classes of Nao sites, cis-inhibited by external Ho, allosterically modified by the binding of H+ to a Hi regulatory site and regulated by Nai. These findings are consistent with Na+/Na+ EXC being a mode of operation of the Na+/H+ exchanger. Na+/H+ EXC was partially inhibited (80-100%) by dimethyl-amiloride (DMA) but basal or pHi-stimulated Na+/Na+ EXC (pHi 6.5, Nai 80 mM) was completely insensitive indicating that Na+/Na+ EXC is an amiloride-insensitive component of Na+/H+ EXC. However, Na+ and H+ efflux into Na-free media were stimulated by cell acidification and also partially (10 to 40%) inhibited by DMA; this also indicates that the Na+/H+ EXC might operate in reverse or uncoupled modes in the absence of Na+/Na+ EXC.(ABSTRACT TRUNCATED AT 400 WORDS)

Diuretics and transmembrane ionic exchanges: structure-activity relations and clinical applications

The study of membrane ion transport has facilitated the discovery of potent and quite specific inhibitory drugs. Some of these compounds are therapeutic agents acting on basic transport mechanisms as in the case of the cardiac glycosides on the myocardial sodium ion (Na+), potassium ion (K+) pump, and the loop diuretics on the renal Na+, K+, chloride (Cl-) co-transport system. The development of inhibitors for other transport systems such as Na+/hydrogen ion (H+), Na+/calcium ion (Ca2+) and bicarbonate (HCO3-)/Cl- exchangers requires the screening of a large number of molecules. For several reasons, the human red blood cell is one of the best models for screening the effect of drugs on ion transport mechanisms. The use of human red cells for pharmacologic studies of ion transport has increased the understanding of the structure-activity relations of diuretics. For instance, loop diuretics that are chemically neutral were considered for many years as drugs that act similarly to classic acid loop diuretics. They are now considered as potent inhibitors of HCO3-/Cl- anion exchange. A brief summary of the more recent results is given together with the perspectives of new fundamental and therapeutic applications of these compounds.

Typology of Na+ transport abnormalities in erythrocytes from essential hypertensive patients. A first step towards the diagnosis and specific treatment of different forms of primary hypertension

Over the last 5 years, several authors have measured apparent affinities and maximal translocation rates of the different erythrocyte Na+ transport systems in essential hypertensive patients. These kinetic studies have clearly shown that no unique red cell Na+ transport defect characterizes the whole population of essential hypertensive patients. Conversely, several complex patterns of erythrocyte Na+ transport abnormalities may be present in different subsets of essential hypertensive patients. These kinetic studies are now providing a more profound biochemical insight into the molecular heterogeneity of primary hypertension. In particular, they may permit the diagnosis and specific treatment of different forms of primary hypertension in the next decade.

Sodium-lithium exchange and sodium-proton exchange are mediated by the same transport system in sarcolemmal vesicles from bovine superior mesenteric artery

Several laboratories have reported that Na+-Li+ countertransport activities are increased in red blood cells from patients with essential hypertension. It has been proposed that the activity of this red blood cell transport system might reflect the activity of a similar system in vascular smooth muscle. We previously demonstrated Na+-Li+ exchange in sarcolemmal vesicles from canine artery and proposed that this transport function might be mediated by the Na+-H+ exchanger. In the present studies, however, we were unable to demonstrate Na+-Li+ countertransport in canine red blood cells. Since bovine red blood cells have a vigorous Na+-Li+ exchanger and we previously demonstrated Na+-H+ exchange in sarcolemmal vesicles from bovine artery, we wished to determine whether bovine sarcolemmal vesicles mediate Na+-Li+ exchange and whether this transport function is mediated via the Na+-H+ exchanger. We found that an outwardly directed proton or Li+ gradient stimulated 22Na+ uptake in sarcolemmal vesicles from bovine superior mesenteric artery. Li+ gradient-stimulated Na+ uptake was not due to electrical coupling between the two ions, was not affected by a change in membrane potential, and could not be explained by the parallel operation of Li+-H+ and Na+-H+ exchange. External Li+ inhibited proton gradient-stimulated Na+ uptake, and external protons inhibited Li+ gradient-stimulated Na+ uptake. Na+ efflux from vesicles was stimulated by inwardly directed gradients for Li+ or protons, and these effects were not additive. Proton efflux from vesicles was stimulated by inwardly directed gradients for Na+ or Li+, and these effects were not additive. Finally, Na+-H+ exchange and Na+-Li+ exchange in sarcolemmal vesicles were inhibited by 5-(N-ethyl-N-isopropyl)amiloride in an identical dose-dependent manner. In conclusion, Na+-Li+ countertransport could not be demonstrated in canine red blood cells, but as is the case with bovine red blood cells, sarcolemmal vesicles from bovine artery mediate Na+-Li+ countertransport. This transport function and sarcolemmal Na+-H+ exchange are mediated via a single 5-(N-ethyl-N-isopropyl)amiloride-sensitive cation exchanger with affinity for Na+, Li+, and protons. The cow, as opposed to the dog, may be a good animal model to test whether the activity of red blood cell Na+-Li+ countertransport is predictive of the activity of Na+-Li+ (and Na+-H+) exchange in vascular smooth muscle.

A study of the transport of lithium across the erythrocyte membrane in vivo and of the effects of the ion transport inhibitors digoxin and dipyridamole

1. We have given an oral load of lithium carbonate to healthy volunteers in order to investigate the transport of lithium across the erythrocyte membrane in vivo and the effects of known inhibitors of that transport. 2. Using this technique we have shown that pretreatment with either digoxin, an inhibitor of the sodium/potassium pump, or dipyridamole, an inhibitor of the anion transporter, does not alter the plasma or erythrocyte lithium concentration profiles, nor any of the pharmacokinetic variables derived from these data, and we conclude that these two transport pathways do not contribute significantly to the in vivo handling of lithium by erythrocytes. 3. We have also shown that erythrocyte lithium concentrations measured directly differ significantly from the predicted concentrations calculated using the two-compartment pharmacokinetic model which has been used in some earlier comparisons of in vitro and in vivo lithium handling. 4. We suggest that the in vivo administration of lithium carbonate may permit a specific measure of the in vivo activity of the sodium/sodium countertransport pathway.

Red-cell sodium-lithium countertransport and fractional excretion of lithium in normal and hypertensive humans

To examine the relations between erythrocyte sodium-lithium countertransport and renal proximal tubular sodium handling, we measured countertransport, and then subjected 30 normal and 32 hypertensive subjects, both white and black, to provocative maneuvers of volume expansion and contraction. The fractional excretions of sodium and lithium were measured simultaneously. In agreement with previous studies, we found that countertransport in erythrocytes was elevated in hypertensive patients compared with normal subjects. We also observed that whites have a higher level of countertransport than blacks. In the basal state, we found that fractional sodium excretion of hypertensive patients was no different than in normal subjects, whereas the fractional lithium excretion of hypertensive persons was increased compared with normotensive values. Volume expansion with 2 1 0.9% saline administered intravenously during a 4-hour period provoked an exaggerated natriuresis and a greater increase in fractional lithium clearance in hypertensive patients compared with the control group. With volume expansion and contraction, fractional lithium clearance and countertransport were directly correlated. Our data suggest that hypertensive persons do not have increased proximal tubular sodium reabsorption compared with normal subjects. Further, the exaggerated natriuresis of hypertension is, in part, the result of increased distal solute delivery. The fact that our hypertensive patients were older may partially explain the discrepancies between this report and previous observations.

Mixture analysis of erythrocyte lithium-sodium countertransport and blood pressure

This study employs multivariate normal mixture analysis, a technique for identifying discrete subgroups within populations, to examine the relation of erythrocyte lithium-sodium (RBC Li+-Na+) countertransport and blood pressure in a group of 474 healthy adults. After adjusting for effects of age, gender, race, height, and weight, univariate mixture analysis of the distribution of mean arterial blood pressure (MAP) revealed the presence of only one group, whereas the distribution of RBC Li+-Na+ countertransport values was composed of a mixture of two groups (p less than 0.00005). When bivariate mixture analysis was applied to the combined distribution of MAP and RBC Li+-Na+ countertransport, two commingled subgroups were identified (p less than 0.00005). The smaller group (19%) had significantly higher values for both MAP (108.7 +/- 16.7 mm Hg, mean +/- SD) and RBC Li+-Na+ countertransport (0.455 +/- 0.147 mmol Li+/l cells.hr) than the larger (81%) group (MAP 93.3 +/- 12.2 mm Hg, RBC Li+-Na+ countertransport 0.247 +/- 0.080 mmol Li+/l cells.hr, p less than 0.0001 for both differences). The relation of MAP to RBC Li+-Na+ countertransport was distinctly different in these two subgroups. In the larger group, we found a weak positive (r = 0.21, p less than 0.0001) correlation for unadjusted values, which was not significant after adjustment. The smaller group, with higher levels of MAP and RBC Li+-Na+ countertransport, showed significant negative correlations for both unadjusted (r = -0.28, p less than 0.008) and adjusted (r = -0.41, p less than 0.0001) values.

Hypertension, non-insulin-dependent diabetes, and intracellular sodium metabolism

The present study was designed to investigate whether non-insulin-dependent diabetic hypertensive patients exhibit abnormalities in intracellular sodium metabolism similar to those described for essential hypertensive patients. Both normotensive and hypertensive non-insulin-dependent diabetic patients had similar average values of both Na+-Li+ countertransport and Na+-K+ cotransport compared with nondiabetic controls. Within the group of diabetic patients, hypertensive patients did not exhibit any abnormalities in either of the sodium transport pathways studied. The possible implications of these findings are addressed.